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Why NASA's Europa Clipper mission to Jupiter's icy moon is such a big deal
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By Conor Feehly published 4 hours ago
The Europa Clipper Mission will analyze the Jovian moon in unprecedented detail, and scientists are excited about what the spacecraft might uncover.

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A spacecraft seen over a red-streaked world. Jupiter, a striped and
swirly looking world, is in the background, offscreen.
An illustration of the Europa Clipper over its icy moon target. (Image
credit: NASA)
In October this year, NASA and the European Space Agency (ESA) will
launch one of the most sophisticated spacecraft ever assembled. Its destination? Europa, Jupiter's fourth largest moon.

The Europa Clipper mission, which aims to reach Europa by 2030, is
stacked with a number of instruments that can help scientists understand
the moon's complex geology and composition — ultimately, researchers
want to use these tools to get a better idea of Europa's habitability.
In other words, they want to learn whether this moon has favorable
conditions for life to exist (life as we know it, at least).

"Jupiter's moon Europa may create the conditions for life in its global
ocean," Steve Vance, an astrobiologist from NASA's Jet Propulsion
Laboratory, said at the Astrobiology Science Conference 2024.

Related: NASA's Juno probe captures fascinating high-resolution images
of Jupiter's icy moon Europa

Recently, a number of scientists involved in different aspects of the
mission spoke at the Astrobiology Science Conference 2024, which is a conference that brings members of the astrobiology community together to collaborate and exchange knowledge. They explained in fascinating detail
how the spacecraft will reach its destination, what the mission might
reveal about Europa's environment, and why the explorer's instruments
may offer tantalizing clues to the presence of life.

"Europa Clipper is the first mission designed to investigate the
habitability of an ocean world," Vance said during the conference.

So, let's get into the promise of this icy world sitting (on average)
444 million miles away from us.

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Europa's possible ocean
It all began with the launch of the Galileo Mission in 1989, which
involved a spacecraft orbiting Jupiter for eight years.

Thanks to Galileo's flybys of the major Jovian moons — Io, Europa,
Callisto and Ganymede — scientists became aware that Europa likely
harbored a liquid ocean beneath its icy exterior surface. This was an incredibly exciting find because, at the time, scientists were unaware
of the presence of liquid water anywhere in our solar system other than
on Earth. The discovery had expanded our understanding of the scope of habitability in our solar system, as it proved liquid water could exist
outside the parameters of the so-called "Goldilocks zone" — the area
around a star where liquid water can exist. Ever since, planetary
scientists have been itching to get back to Europa.

"We are going to try to characterize the ocean using magnetic fields,"
Vance explained at the conference.

"Galileo, a previous spacecraft, flew by Europa four times, close enough
to get a magnetic response," Vance said. "This is like Europa walking
through a metal detector at an airport, except Jupiter is the metal
detector which creates this field that Europa responded to."

Scientists have designed the Europa Clipper mission to conduct multiple
flybys of Europa in order to sample different aspects of the moon's
magnetic response. On one hand, researchers will try to figure out the response's strength, and on the other, they'll attempt to measure the
timing of the response relative to Jupiter's magnetic field. "Through
this, we hope to work out the salinity of the ocean," said Vance.

A rocky world's surface. Beyond the horizon, Jupiter looks huge. Toward
the top left, there's a hazy star.

This artist's concept shows a simulated view from the surface of
Jupiter's moon Europa. Europa's potentially rough, icy surface, tinged
with reddish areas that scientists hope to learn more about, can be seen
in the foreground. The giant planet Jupiter looms over the horizon.
(Image credit: NASA/JPL-Caltech)
Europa's chemistry
Though the possibility of confirming the presence of liquid water on
Europa is certainly exciting in and of itself, researchers also want to
get a better understanding of other processes on the moon that could
impact its potential habitability.

For example, the exterior of Europa is exposed to high levels of
radiation from charged particles trapped in Jupiter's magnetosphere.
Under standard circumstances, scientists would expect such a surface to
likely be inhospitable to life. However, it's also possible that
radiation may contribute to Europa's habitability. This is because
radiation exposure on the moon's surface can break down water molecules
into its constituents, oxygen and hydrogen. Astrobiologists are
interested in whether these resulting oxygen atoms from the surface of
Europa can mix with the salty ocean beneath via the drainage of
near-surface brines through cracks in the surface. To reach that
conclusion, however, scientists would need to understand the dynamics
and thickness of the moon's ice sheet.

Thankfully, Europa Clipper is on the case.

The spacecraft will have a suite of imaging instruments to help deduce
the geological processes occurring on the moon's surface; one such
instrument is ice-penetrating radar that can help determine the ice
shell's thickness. This will give researchers an idea of how permeable
the boundary is between Europa's surface and interior.

A grayish, scarred word is seen half lit, hanging in space.

A view of Jupiter's moon Europa captured by NASA's Juno mission during
its Sept. 29 close flyby at the moon. The spacecraft was 945 miles
(1,500 kilometers) above the moon's surface when the image was taken.
(Image credit: NASA/JPL-Caltech/SwRI/MSSS. Image processing by Björn
Jónsson CC BY-NC-SA 2.0)
"Europa's surface is very geologically interesting, and has likely been
active for a very long time. It might not be that thick, and there may
be materials for life just beneath the surface," said Vance.

Oxygen, for instance, is a reactive element. This means oxygen
transported from Europa's surface to its interior could potentially be
used in subsurface chemical reactions that generate energy. Those
reactions, if in occurrence, would happen because of microbial life
living in the ocean because those microbes wouldn't have access to
sunlight for energy.

The interaction of water and rock deep within Europa may also release
hydrogen and other chemicals into the ocean. And, because Europa is
constantly flexing due to massive tidal forces as it orbits Jupiter, the interior of the moon is likely warm. That means hydrothermal vents may
be supplying the ocean floor with chemical nutrients, similar to the way
vent systems found on Earth's ocean floor work.

A rounded triangular plate with lots of wavelength designs.

The engraved art on the outward-facing side of the Europa Clipper vault
plate, which will help shield the spacecraft's electronics from
radiation, features visual representations of the sound waves formed by
the word "water" in 103 languages. (Image credit: NASA/JPL-Caltech)
Hunting for biosignatures
As researchers and engineers don't currently have enough information
about Europa's surface features, landing on the Jovian moon, at least
for this mission, is out of the question.

This means researchers will be limited by what they can see and collect
from orbit when the spacecraft reaches Europa. Because any potential
life lurking on Europa is likely in its interior, researchers will
instead be looking for deductive signs noticeable on the surface and in
its atmosphere.

The Europa Clipper possesses a range of instruments which will gather
materials ejected from icy geysers on the moon, and those materials
could provide astrobiologists with credible evidence that living
processes are indeed occurring beneath the surface.

Astrobiologists usually refer to such evidence as "biosignatures." A biosignature is a chemical byproduct of living processes. For example,
high oxygen levels in Earth's atmosphere can be considered a
biosignature generated by plants. However, what might be considered a biosignature in one context might not be in another. A recent example of
this was the detection of traces of phosphine, a possible biosignature,
in the atmosphere of Venus. On Earth, phosphine is a byproduct of
anaerobic ecosystems, which led some to suspect Venus of having
anaerobic organisms living in its atmosphere. However, researchers later revealed that the phosphine in Venus' atmosphere could be generated from volcanism.

Non-living processes are also capable of producing chemicals we usually associate with living processes, muddying what we might consider as
signs of life. This means any possible biosignature has to make sense in
the context of the system it's found within.

In the context of Earth, oxygen is constantly being replenished in our atmosphere by algae, cyanobacteria and plants. To anyone looking at
Earth's atmosphere from afar, our high oxygen levels would be an
indication that there is some interesting chemistry happening, because
the oxygen in our atmosphere wouldn't last long if it wasn't being
replenished (due to its high reactivity). However, if someone was
looking for oxygen as a sign of life in Earth's atmosphere before the
onset of the Great Oxygenation Event 2.4 billion years ago, they would
be out of luck. Earth would look ordinary, despite being home to life.

"There's been lots of work done to understand what kind of chemical biosignatures exist and how to detect them … we kind of think of life as
a binary thing, but detecting life is not necessarily binary, or easy,
at all," Elizabeth "Zibi" Turtle from Johns Hopkins Applied Physics
Laboratory said at the conference. Turtle leads the Europa Imaging
System (EIS) on Europa Clipper.

A fast-forwarded gif of scientists working on the Clipper.

NASA's Europa Clipper spacecraft that will search for traces of life on Jupiter's ice-covered moon Europa being assembled at the agency's Jet Propulsion Laboratory in California. (Image credit: NASA)
One of the most exciting pieces of tech the Europa Clipper is carrying
on its voyage to the Jovian system is the Mass Spectrometer for
Planetary Exploration, or MASPEX. MASPEX will collect gases and
molecules in what exists of Europa's atmosphere during the spacecraft's
close flybys.

How does it work? The instrument bombards the materials it will scoop up
from Europa's atmosphere with high-energy electrons (negatively charged particles), which strips the collected materials of their own electrons.
This turns the captured molecules into positively-charged ions. An atom
or molecule becomes ionized when it becomes a more positively or more negatively charged version of itself, which can happen if it acquires or
loses electrons or protons, the latter of which are positively charged particles.

The ions produced by MASPEX can then be accelerated around a "drift
tube" that's also on the apparatus, where lighter ions move faster
around the tube. The speed at which the ions move in the tube will
therefore give scientists an idea of their masses, and, in turn, their identities.

RELATED STORIES:
— NASA Juno spacecraft picks up hints of activity on Jupiter's icy moon Europa

— Jupiter's ocean moon Europa may have less oxygen than we thought

— Watch this Jupiter moon lander handle harsh terrain it may face on
Europa (video)

"While the goal is to understand the chemistry that directs Europa,
including the possible metabolisms that might happen in Europa's oceans,
the mass spectrometer, and the dust analyzer as well, have the
possibility of picking up large organic molecules including amino acids
and things that might be clues to the presence of life — though not definitive evidence of life itself," said Vance at AbSciCon2024.

If MASPEX is able to identify organic molecules or even amino acids, as
well as offer an indication that materials from the moon's surface have
a clear pathway to the ocean beneath, this will give researchers a huge
reason to be optimistic about the chances of life on Europa.

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Conor Feehly
Conor Feehly
Contributing Writer
Conor Feehly is a New Zealand-based science writer. He has earned a
master's in science communication from the University of Otago, Dunedin.
His writing has appeared in Cosmos Magazine, Discover Magazine and ScienceAlert. His writing largely covers topics relating to neuroscience
and psychology, although he also enjoys writing about a number of
scientific subjects ranging from astrophysics to archaeology.

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